An adjacent sibling selector can be used to select an element that follows another element where both elements share the same parent element. The adjacent sibling elements are separated by a plus (+) sign.

The following HTMLW page demonstrates adjacent sibling selectors. It features two adjacent sibling selectors, 'h1+h2' and 'h2+h1'. The first rule states to turn the text red for an h2 element that follows an h1 element. The second rule states to turn the text blue for an h1 element that follows an h2 element.